Multi-stress electrical and thermal ageing of HV XLPE cables: physical and chemical determinants of cable insulation ageing

This paper examines developments in the study of the ageing of polymeric materials subject to long term electrical and thermal ageing. These demonstrate the need to understand and model heterogeneous ageing, localised degradation processes and progressive damage accumulation that can lead to defect propagation and catastrophic failure. It is shown that microscopic TEM analysis complemented with optical microscopy is an effective, if laborious, way of determining the mesoscopic to microscopic void distribution in XLPE cable insulating materials. AFM studies are useful in sampling the detailed topology of void shapes but as the voids are present in relatively low concentrations AFM is too time consuming to use it to obtain reliable statistics. In contrast, small-angle X-ray scattering can be used to access the nano-void distribution and is being used in European Commission funded project called ARTEMIS to complement TEM. However, determination of the true nanovoid concentration by SAXS is dependent on correctly accounting for the crystal phase scattering.